Convert MKV to MP3 — Free Online Tool
Extract and convert the audio track from an MKV file into a universally compatible MP3 using the LAME encoder. Whether your MKV contains AAC, Opus, Vorbis, or FLAC audio, this tool transcodes it directly to MP3 — no video stream, no bloat.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your MKV file here
or click to browse
Free — no uploads, no signups. Your files never leave your browser.
Settings
Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
MKV is a container that can hold virtually any audio codec, so the audio stream inside your MKV must be decoded and re-encoded to MP3 using the LAME encoder (libmp3lame). The video stream is discarded entirely — this is an audio extraction, not a remux. The FFmpeg command reads the first audio track from the MKV, transcodes it to lossy MP3 at 128k bitrate by default, and writes a standalone .mp3 file. Because every MKV audio codec (AAC, Opus, Vorbis, FLAC) requires decoding before LAME can encode it to MP3, full transcoding always occurs — there is no stream-copy shortcut here. ID3 tags from MKV metadata may be partially carried over depending on what metadata fields the MKV container stored.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program. In the browser-based tool, this runs via FFmpeg.wasm compiled to WebAssembly, so no installation is required and no files leave your device. |
-i input.mkv
|
Specifies the input file — your MKV source. FFmpeg inspects the Matroska container and identifies all streams inside it, including video, audio, subtitles, and chapters, before processing begins. |
-c:a libmp3lame
|
Instructs FFmpeg to encode the audio stream using the LAME MP3 encoder (libmp3lame), which is the industry-standard library for producing MP3 files. Since MP3 supports only this codec, this flag is non-negotiable for the output format. |
-b:a 128k
|
Sets the audio bitrate to 128 kilobits per second, which is the standard default for MP3 — adequate for speech and general music listening. Increase to 192k or 320k for higher fidelity, especially if the MKV source audio was lossless FLAC. |
output.mp3
|
Defines the output filename and its .mp3 extension, which signals FFmpeg to write a bare MP3 bitstream. Unlike the MKV input, this output file holds only audio data and ID3 tag metadata — no video, subtitles, or chapters. |
Common Use Cases
- Ripping the audio from an MKV movie or TV episode rip to create a standalone audio file for listening during a commute without needing a video player
- Extracting music or a live concert recording stored in MKV format to load onto an MP3 player or older car stereo that does not support MKV or Opus audio
- Pulling the audio track from an MKV screen recording or tutorial video to produce a podcast episode or audio-only version of a presentation
- Converting an MKV audiobook or lecture recording downloaded from a video platform into MP3 so it can be imported into podcast apps like Overcast or Pocket Casts
- Extracting dialogue or sound effects from an MKV video project asset library into MP3 files for use in audio editing software like Audacity or GarageBand
- Stripping audio from a large MKV anime or foreign film file to share just the soundtrack or opening theme as a small MP3 without redistributing the full video
Frequently Asked Questions
Yes — MP3 is a lossy format, so some audio information is discarded during encoding. If your MKV already contains a lossy audio track (such as AAC or Opus), converting to MP3 means a second generation of lossy compression, which can introduce subtle artifacts. If the source audio is lossless FLAC inside the MKV, you'll experience quality loss for the first time during this conversion. At 128k bitrate the result is perceptually acceptable for speech and most music, but audiophiles should consider using 192k or 320k for better fidelity.
Both are discarded. MP3 is a pure audio format with no container structure capable of holding video streams, subtitle tracks, chapter markers, or multiple audio tracks. Only the first audio track from the MKV is transcoded. If your MKV has multiple audio tracks (for example, English and Japanese dubs), only the default or first track is extracted — you would need to specify a different track using FFmpeg's -map flag to target a specific stream.
Replace the value after -b:a in the command. For example, to encode at 320k (the highest standard MP3 bitrate), use: ffmpeg -i input.mkv -c:a libmp3lame -b:a 320k output.mp3. Common choices are 128k for general use, 192k for better quality music, and 320k for the highest quality MP3. Lowering to 96k or 64k will reduce file size significantly but introduces more noticeable compression artifacts, especially in music with high-frequency content.
Yes, on the command line you can use a shell loop to process multiple files. On Linux or macOS: for f in *.mkv; do ffmpeg -i "$f" -c:a libmp3lame -b:a 128k "${f%.mkv}.mp3"; done. On Windows Command Prompt: for %f in (*.mkv) do ffmpeg -i "%f" -c:a libmp3lame -b:a 128k "%~nf.mp3". The browser-based tool processes one file at a time, so the command-line approach is recommended for bulk conversions.
Partially. FFmpeg will attempt to map compatible MKV metadata fields (such as title, artist, and album) to ID3 tags in the MP3 output. However, MKV metadata is stored in Matroska's own tag format, and not all fields have direct ID3 equivalents. Chapter data and subtitle metadata are completely dropped since MP3 has no support for those structures. You may want to verify and edit the ID3 tags in the output file using a tool like MP3Tag after conversion.
Because the video stream — which typically accounts for 80–95% of an MKV file's size — is entirely removed. Only the audio is kept and re-encoded as MP3. A 2GB MKV movie with a 128k MP3 audio track will typically produce an MP3 file under 100MB. The exact output size depends on the audio duration and the bitrate you choose: at 128k, one hour of audio produces roughly 56MB.
Technical Notes
MKV files commonly carry audio in AAC, Opus, Vorbis, or FLAC — none of which can be stream-copied into an MP3 container, since MP3 supports only the MPEG Audio Layer III codec encoded by libmp3lame. Full decoding and re-encoding is therefore mandatory regardless of the source codec. One consequence is that if the source is Opus or AAC at a low bitrate, transcoding to MP3 at the same or lower bitrate will compound compression losses; in those cases, use the highest practical output bitrate (192k–320k) to minimize artifacts. MKV's support for multiple audio tracks means FFmpeg will default to the first audio stream unless you explicitly use -map 0:a:1 (or similar) to select a different track. Chapter markers, subtitle streams, and video streams are automatically excluded because the MP3 format has no mechanism to store them — no special flag is needed to drop them. LAME's variable bitrate mode (VBR) is an alternative to the constant bitrate (-b:a) used here; you can substitute -q:a 2 for near-320k quality VBR output, which often yields smaller files than CBR 320k at equivalent perceived quality.